We propose to study the role of glutathione reductase, glutathione peroxidase, and glucose-6-phosphate dehydrogenase in maintaining platelet function. These enzymes have been selected for study because several lines of evidence indicate that adequate levels of intercellular and membrane SH-groups are necessary for the platelet to perform its role in hemostasis. Steady state kinetic methods will be used to investigate the kinetic and regulatory properties of these enzymes. These studies will enable us to discover modifiers of the enzymes and thus allow us to alter their inter-cellular activity. The effect of this altered enzyme activity on platelet function will be tested by measuring ADP-induced aggregation, clot retraction and serotonin uptake.